Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
  • C09K3/1409—Abrasive particles per se
  • C09K3/1418—Abrasive particles per se obtained by division of a mass agglomerated by sintering
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
  • C04B35/111—Fine ceramics
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
  • C04B35/111—Fine ceramics
  • C04B35/1115—Minute sintered entities, e.g. sintered abrasive grains or shaped particles such as platelets
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
  • C09K3/1409—Abrasive particles per se

Definitions

• This invention relates to aluminous abrasive grits and particularly to sol-gel alumina abrasive materials with improved grinding performance.
• Sol-gel alumina abrasives are conventionally produced by drying a sol or gel of an alpha alumina precursor which is usually but not essentially, boehmite; breaking up the dried gel into particles of the desired size; then firing the pieces to a temperature sufficiently high to convert them to the alpha alumina form.
• Simple sol-gel processes are described for example in USPP 4,314,827; 4,518,397; 4,881,951 and British Patent Application 2,099,012.
• the alpha alumina precursor is "seeded” with a material having the same crystal structure as, and lattice parameters as close as possible to, those of alpha alumina itself.
• the “seed” is added in as finely divided form as possible and is dispersed uniformly throughout the sol or gel. It can be added ab initio or it can be formed in situ.
• the function of the seed is to cause the transformation to the alpha form to occur uniformly throughout the precursor at a much lower temperature than is needed in the absence of the seed.
• This process produces a crystalline structure in which the individual crystals of alpha alumina, (that is those areas of substantially the same crystallographic orientation separated from adjacent crystals by high angle grain boundaries) , are very uniform in size and are essentially all sub-micron in diameter.
• Suitable seeds include alpha alumina itself but also other compounds such as alpha ferric oxide, chromium suboxide, nickel titanate and a plurality of other compounds that have lattice parameters sufficiently similar to those of alpha alumina to be effective to cause the generation of alpha alumina from a precursor at a temperature below that at which the conversion normally occurs in the absence of such seed.
• Examples of such seeded sol-gel processes are described in USPP 4,623,364; 4,744,802; 4,954,462; 4,964,883; 5,192,339; 5,215,551; 5,219,806 and many others.
• sol-gel alumina abrasive grit which comprises from about 0.01% to about 2% by weight of an oxide selected from the group consisting of rubidium oxide, caesium oxide and mixtures thereof.
• a sol-gel alumina which comprises from about 0.1 to about 20% of an oxide selected from the group consisting of magnesium oxide and zir_:onia and mixtures thereof, and from about 0.01% to about 2 % by weight of an oxide selected from the group consisting of rubidium oxide, caesium oxide and mixtures thereof.
• the sol-gel alumina is a seeded sol-gel alumina and comprises from about 2 to about 10% of magnesium oxide and from about 0.05 to about 1% by weight of an oxide selected from the group consisting of rubidium oxide, caesium oxide and mixtures thereof.
• the seed used is preferably alpha alumina.
• the seed should be as finely divided as practically possible in order to achieve the greatest possible number of nucleating sites for a given weight of seed. Generally seed that is smaller than about 0.1 micron and more preferably less than about 0.05 micron is selected. If the contamination of the alumina is not a problem, it is also possible to use alpha ferric oxide or a material that yields the oxide upon heating such as the "hydrous iron polymer" used in USP 4,954,462 which readily generates seed in a very finely divided form upon heating.
• the total amount of rubidium oxide, caesium oxide or mixture of these oxides present in the sol-gel alumina abrasives of the invention may be from about 0.01 to about 2%, preferably from about 0.03 to about 1% and most preferably from about 0.05 to about 0.5% based on the total weight of alumina in the abrasive grain.
• the rubidium or caesium oxide performs particularly well when it is present together with magnesium oxide.
• the magnesium oxide is most often present in the form of a spinel and the total amount, calculated as MgO, can be from about 0.1 to about 20% and more preferably from about 0.5 to about 15% of the total weight of alumina in the abrasive grain. Description of Preferred Embodiments The invention is now described in terms of certain formulations within the scope of the invention. These are not however to be taken as indicating any necessary limitation on the essential scope of the invention.
• Example 1 (Comparative) 7,000 gm of boehmite, ("Disperal" obtainable under that trade name from Condea Gmbh) , was mixed in a Ross mixer with 50,000 gm of deionized water and 2,333 gm of a 6% solids aqueous slurry of alpha alumina particles with a surface area of about 120 m 2 /gm. The dispersion was continuously mixed under vacuum.
• Example 1 The formula of Example 1 was followed exactly except that 25.2 gm of a 5% solution of rubidium nitrate was mixed with 17,275 gm of the gel before it is dried.
• abrasive grits obtained from Examples 1 and 2 were tested for their abrasive properties in a coated abrasive structure with the grits held by a phenolic resin. The results of two duplicate runs are set forth in Table 1 below.
• Example 3 (Comparative) 900 kg of water were added to a mixing tank and 118 kg of an aqueous slurry containing 4% by wt. of alpha alumina seed having a BET surface area of about 120 ⁇ r/gm were added along with 567 kg of boehmite, ("Disperal" available under that trade name from Condea GmbH), and 40.5 kg of 21% nitric acid. The mixture was then mixed with a high-speed disperser blade and evacuated to eliminate air bubbles. The pH of the mixture was about 4.
• This dispersion was then homogenized by passage through an in-line homogenizer at a rate of 10.6 litres/minute along with 0.6 litres/minute of 21% nitric acid.
• the resulting gel was dried, roll-crushed and sintered in a pre-heated rotary furnace at about 1300°C for about 10 minutes.
• This material was screened to a 50T grit size for testing in a coated abrasive product. (See Table 2 below) .
• Example 4 A dispersion of 14,850 gm of Condea "Disperal" in 100,000 gm of deionized water in a Ross Mixer were mixed with 4950 gm of a 6% solids slurry of alpha alumina seeds having a BET surface area of about 120 m 2 /gm. The dispersion was maintained under vacuum while being continuously agitated. A solution of 1060 gm of 70% nitric acid in 10,000 gm of deionized water.
• This dispersion was in sol-gel form and this was mixed for a further 5 minutes before being dried.
• This dried gel was then broken up into smaller than 0.5 to 1 cm pieces which were then fired at about 1330°C in a pre-heated rotary furnace having a silicon carbide tube 15 cm in diameter and 215 cm long with a hot zone about 61.6 cm long inclined at 6° to the horizontal and rotating at about 12 rpm.
• the fired grains had a density of greater than 3.8 gm/cc and were made up of crystals less than 0.2 micron in diameter as measured by the average intercept method.
• the grits were screened to a 50T size and used to make a coated abrasive product.
• the abrasion performance of the products of Examples 3 and 4 were evaluated in the form of abrasive belts 150 cm long by 6.25 cm wide, containing 590 gm of grits per square meter, in which the grits were held in phenolic resin maker and size coats.
• the belts were tested in a fixed force mode running at a linear speed of 900 surface meters/minute under an aqueous coolant.
• the cut time was four minutes and the material cut was a stainless steel bar held against the belt at a force of 6.75 kg.
• the total grams of the steel cut in the test were measured. Table 2
• Example 5 A grain similar to that prepared in Example 1 (Comparative) was prepared with the difference that 25.5 g of a 5% solution of rubidium nitrate was mixed with 17275 g of the gel before the gel was dried and fired to form the abrasive grits. In all other respects the procedure was identical.
• the grain produced according to the processes of Examples 1, 3 and 5 were compared as to grinding performance in a coated abrasive test rig in which grit (-45+50 mesh) were retained by phenolic resin maker and size coats. A supersize coat containing KBF was added to each. Identical amounts of grit, maker, size and supersize coats were used in each case.
• the test rig was used to cut 304 stainless steel using a water-based coolant and grinding was continued until cutting was no longer detected. In each case the total amount of steel cut was measured. The results are set forth in Table 3 below.
• Example 6 A further product according to the invention was prepared by a process in which 14,850 g of Condea's "Disperal" boehmite was mixed with 100,000 g of deionized water in a Ross mixer. To this mixture were added 4,959 g of a 6% solids slurry of alpha alumina seeds with a surface area of about 120 m 2 /g. As the mixture was kept continuously stirred under vacuum, a solution of 1,060 g of 70% nitric acid in 10,000 g of deionized water was added followed by a further 10 minutes of mixing.
• the grits were screened to 50T size and used to make a conventional coated abrasive belt which was then used to grind 304 stainless steel in a fixed force mode test. An aqueous coolant was used as the belt was used to cut the steel for 20 minutes under a fixed force of 6.75 kg. The total steel cut at the end of this time was measured.
• Example 7 110,000 gm of deionized water were added to a Ross mixer followed by 3,960 gm of a 6% solids slurry of alpha alumina seed having a surface area of about 120 m 2 /gm. This mixture was mixed while 14,850 gm of Disperal from Condea GmbH were added. Mixing under vacuum was continued for 5 minutes. A solution of 1,060 gm of 70% nitric acid in 10,000 gm of deionized water were then added and mixing under vacuum was continued for a further 10 minutes.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Ceramic Engineering (AREA)
• Structural Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Catalysts (AREA)
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• 1995
  • 1995-04-05 US US08/417,323 patent/US5516347A/en not_active Expired - Lifetime
• 1996
  • 1996-03-12 TW TW085102968A patent/TW380122B/zh not_active IP Right Cessation
  • 1996-03-13 CN CN96193052A patent/CN1073611C/zh not_active Expired - Fee Related
  • 1996-03-13 AU AU52515/96A patent/AU686945B2/en not_active Ceased
  • 1996-03-13 DK DK96908793T patent/DK0819153T3/da active
  • 1996-03-13 EP EP96908793A patent/EP0819153B1/en not_active Expired - Lifetime
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  • 1996-03-13 WO PCT/US1996/003437 patent/WO1996031575A1/en active IP Right Grant
  • 1996-03-26 ZA ZA962405A patent/ZA962405B/xx unknown

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